1. Field of the Invention
The present invention relates to a sealing means for a subsurface chamber for establishing a liquid tight seal against an inner cylindrical surface of a wall of the chamber.
2. Description of the Prior Art
Aircraft docking areas at many air terminals are often provided with subsurface aircraft servicing pits located beneath the tarmac across which the wheels of aircraft roll while the aircraft are on the ground. Subservice aircraft servicing pits have the distinct advantage over mobile land vehicles used to service aircraft in that subsurface aircraft servicing pits do not provide obstacles to docking and departing aircraft and do not interfere with the maneuvering of aircraft in docking and refueling areas.
Conventional subsurface aircraft servicing pits are frequently formed as prefabricated fiberglass enclosures having hinged aluminum or steel access doors and hatches to allow access from above. The access doors are located flush with the surface of the aircraft loading and refueling aprons. Fuel pipes, electrical lines and conduits for supplying heated and cooled air emanate from central supply sources within an air terminal and extend underground beneath the aircraft loading and refueling aprons and into subsurface aircraft servicing pits, often through the bottom of a pit. The pit is often formed with a cylindrical interior wall surface, and is positioned so that the cylindrical wall surface surrounds a riser pipe which extends up into the pit through an open bottom therein.
When fuel pipes or other supply lines are brought into subsurface aircraft servicing pits they are terminated at valves or hydrants within the pits. Since aircraft fuel can be a form of toxic waste, if released into the environment, it is important to seal the bottom opening of the pit beneath the ground to prevent any spilled aircraft fuel from leaking out of the pit and into ground water. To this end, the bottoms of aircraft servicing pits are conventionally lined with moisture or ground seals that extend from the walls of the pit to the outer surfaces of the pipes and ducts which enter through openings through the floor of the pit and which terminate within the pit. Often fuel is brought into the pit by a single, vertically oriented riser pipe that branches from a lateral pipe line and extends vertically upwardly through the open bottom of an aircraft servicing pit.
Because the bottom of the pit is open, it is necessary to provide a seal that extends across the annular space between the outer cylindrical convex surface of a conventional riser pipe and the inner cylindrical concave surface of the pit wall. To provide a moisture proof seal to prevent fuel from leaking through the bottom of the pit, an annular expanse of a moisture impervious material, such as Buna-N rubber is spread across the bottom of the pit and is sealed to both the cylindrical outer surface of the riser pipe and the cylindrical inner surface of the pit wall. However, while reliable ground seals can be established to attach the inner peripheral margin of the sealing boot against the outer convex surface of a riser pipe, attempts to seal the outer peripheral margin of the boot against the concave interior cylindrical surface of the pit wall have proven unsatisfactory. The seals attempted have not been reliable, and liquid can leak past such conventional seals through the interface between the outer peripheral margin of the boot and the concave cylindrical surface of the pit wall.
One approach to a solution of this problem has been to form the bottom of the pit with an annular floor which terminates interiorally of the outer, concave cylindrical wall in an upwardly projecting lip. This upwardly projecting lip is configured into a cylindrical collar disposed about a riser pipe at a sufficient distance therefrom to provide adequate clearance between the riser pipe and the annular lip defining the collar formed in the floor of the pit. A seal can then be established using conventional cinch-type compression band clamps to establish liquid seals between a boot and the outer cylindrical convex surface of the riser pipe and between the boot and the outer convex cylindrical surface of the lip surrounding the opening in the floor of the pit into which the riser pipe projects. One such sealing system is described in U.S. Pat. No. 4,850,389, issued July 25, 1989.
A pit constructed to provide a convex surface against which a conventional cinch-type compression band clamp bears to clamp a rubber boot into position is not an open bottom pit in the true sense of the term. To the contrary, the bottom is to a large extent closed by the annular floor defined therein. Such a pit construction increases the cost of fabrication of the pit significantly, as contrasted with the cost of fabricating a simple, cylindrical open bottom pit. Moreover, the cost of installation of a pit having a floor with a central opening therein likewise increases significantly, since the central opening in the floor of the pit affords far less clearance about the riser pipe than the much larger diameter of the cylindrical wall of an open bottom pit. It is therefore considerably more difficult to lower the pit precisely into position such that the riser pipe projects upwardly through the relatively small opening in the center of the floor of the pit.
Nevertheless, such floored pit constructions have been adopted to a large extent to establish reliable, liquid tight seals between the structure of the pit and a riser pipe located therewithin.